SHA2(3) | Library Functions Manual | SHA2(3)

# NAME

SHA256_Init, SHA256_Update, SHA256_Pad, SHA256_Final, SHA256_Transform, SHA256_End, SHA256_File, SHA256_FileChunk, SHA256_Data — calculate the NIST Secure Hash Standard (version 2)

# SYNOPSIS

#include <sys/types.h>
#include <sha2.h>

void
SHA224_Init(SHA224_CTX *context);

void
SHA224_Update(SHA224_CTX *context, const uint8_t *data, size_t len);

void
SHA224_Pad(SHA224_CTX *context);

void
SHA224_Final(uint8_t digest[SHA224_DIGEST_LENGTH], SHA224_CTX *context);

void
SHA224_Transform(uint32_t state[8], const uint8_t buffer[SHA224_BLOCK_LENGTH]);

char *
SHA224_End(SHA224_CTX *context, char *buf);

char *
SHA224_File(const char *filename, char *buf);

char *
SHA224_FileChunk(const char *filename, char *buf, off_t offset, off_t length);

char *
SHA224_Data(uint8_t *data, size_t len, char *buf);

void
SHA256_Init(SHA256_CTX *context);

void
SHA256_Update(SHA256_CTX *context, const uint8_t *data, size_t len);

void
SHA256_Pad(SHA256_CTX *context);

void
SHA256_Final(uint8_t digest[SHA256_DIGEST_LENGTH], SHA256_CTX *context);

void
SHA256_Transform(uint32_t state[8], const uint8_t buffer[SHA256_BLOCK_LENGTH]);

char *
SHA256_End(SHA256_CTX *context, char *buf);

char *
SHA256_File(const char *filename, char *buf);

char *
SHA256_FileChunk(const char *filename, char *buf, off_t offset, off_t length);

char *
SHA256_Data(uint8_t *data, size_t len, char *buf);

void
SHA384_Init(SHA384_CTX *context);

void
SHA384_Update(SHA384_CTX *context, const uint8_t *data, size_t len);

void
SHA384_Pad(SHA384_CTX *context);

void
SHA384_Final(uint8_t digest[SHA384_DIGEST_LENGTH], SHA384_CTX *context);

void
SHA384_Transform(uint64_t state[8], const uint8_t buffer[SHA384_BLOCK_LENGTH]);

char *
SHA384_End(SHA384_CTX *context, char *buf);

char *
SHA384_File(char *filename, char *buf);

char *
SHA384_FileChunk(char *filename, char *buf, off_t offset, off_t length);

char *
SHA384_Data(uint8_t *data, size_t len, char *buf);

void
SHA512_Init(SHA512_CTX *context);

void
SHA512_Update(SHA512_CTX *context, const uint8_t *data, size_t len);

void
SHA512_Pad(SHA512_CTX *context);

void
SHA512_Final(uint8_t digest[SHA512_DIGEST_LENGTH], SHA512_CTX *context);

void
SHA512_Transform(uint64_t state[8], const uint8_t buffer[SHA512_BLOCK_LENGTH]);

char *
SHA512_End(SHA512_CTX *context, char *buf);

char *
SHA512_File(char *filename, char *buf);

char *
SHA512_FileChunk(char *filename, char *buf, off_t offset, off_t length);

char *
SHA512_Data(uint8_t *data, size_t len, char *buf);

# DESCRIPTION

The SHA2 functions implement the NIST Secure Hash Standard, FIPS PUB 180-2. The SHA2 functions are used to generate a condensed representation of a message called a message digest, suitable for use as a digital signature. There are four families of functions, with names corresponding to the number of bits in the resulting message digest. The SHA-224 and SHA-256 functions are limited to processing a message of less than 2^64 bits as input. The SHA-384 and SHA-512 functions can process a message of at most 2^128 - 1 bits as input.

The SHA2 functions are considered to be more secure than the sha1(3) functions with which they share a similar interface. The 224, 256, 384, and 512-bit versions of SHA2 share the same interface. For brevity, only the 256-bit variants are described below.

The SHA256_Init() function initializes a SHA256_CTX context for use with SHA256_Update(), and SHA256_Final(). The SHA256_Update() function adds data of length len to the SHA256_CTX specified by context. SHA256_Final() is called when all data has been added via SHA256_Update() and stores a message digest in the digest parameter.

The SHA256_Pad() function can be used to apply padding to the message digest as in SHA256_Final(), but the current context can still be used with SHA256_Update().

The SHA256_Transform() function is used by SHA256_Update() to hash 512-bit blocks and forms the core of the algorithm. Most programs should use the interface provided by SHA256_Init(), SHA256_Update(), and SHA256_Final() instead of calling SHA256_Transform() directly.

The SHA256_End() function is a front end for SHA256_Final() which converts the digest into an ASCII representation of the digest in hexadecimal.

The SHA256_File() function calculates the digest for a file and returns the result via SHA256_End(). If SHA256_File() is unable to open the file, a NULL pointer is returned.

SHA256_FileChunk() behaves like SHA256_File() but calculates the digest only for that portion of the file starting at offset and continuing for length bytes or until end of file is reached, whichever comes first. A zero length can be specified to read until end of file. A negative length or offset will be ignored.

The SHA256_Data() function calculates the digest of an arbitrary string and returns the result via SHA256_End().

For each of the SHA256_End(), SHA256_File(), SHA256_FileChunk(), and SHA256_Data() functions the buf parameter should either be a string large enough to hold the resulting digest (e.g., SHA224_DIGEST_STRING_LENGTH, SHA256_DIGEST_STRING_LENGTH, SHA384_DIGEST_STRING_LENGTH, or SHA512_DIGEST_STRING_LENGTH, depending on the function being used) or a NULL pointer. In the latter case, space will be dynamically allocated via malloc(3) and should be freed using free(3) when it is no longer needed.

# EXAMPLES

The following code fragment will calculate the SHA-256 digest for the string “abc”, which is “0xba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad”.

    SHA256_CTX ctx;
    uint8_t results[SHA256_DIGEST_LENGTH];
    char *buf;
    int n;

    buf = "abc";
    n = strlen(buf);
    SHA256_Init(&ctx);
    SHA256_Update(&ctx, (uint8_t *)buf, n);
    SHA256_Final(results, &ctx);

    /* Print the digest as one long hex value */
    printf("0x");
    for (n = 0; n < SHA256_DIGEST_LENGTH; n++)
    	printf("%02x", results[n]);
    putchar('\n');

Alternately, the helper functions could be used in the following way:

    SHA256_CTX ctx;
    uint8_t output[SHA256_DIGEST_STRING_LENGTH];
    char *buf = "abc";

    printf("0x%s\n", SHA256_Data(buf, strlen(buf), output));

# SEE ALSO

cksum(1), md4(3), md5(3), rmd160(3), sha1(3)

Secure Hash Standard, FIPS PUB 180-2.

# HISTORY

The SHA2 functions appeared in OpenBSD 3.4 and NetBSD 3.0.

# AUTHORS

This implementation of the SHA functions was written by Aaron D. Gifford.

The SHA256_End(), SHA256_File(), SHA256_FileChunk(), and SHA256_Data() helper functions are derived from code written by Poul-Henning Kamp.

# CAVEATS

This implementation of the Secure Hash Standard has not been validated by NIST and as such is not in official compliance with the standard.

If a message digest is to be copied to a multi-byte type (i.e.: an array of five 32-bit integers) it will be necessary to perform byte swapping on little endian machines such as the i386, alpha, and vax.

May 20, 2009 | NetBSD 7.2